A boost regulator receives a voltage from an unregulated voltage source, such as a bank of batteries, and generates a higher constant voltage at an output terminal. Relatively high voltages are needed for devices such as digital cameras and display drivers.
The control portion of a boost regulator is typically implemented as an integrated circuit. The boost regulator switches a switching transistor at a certain frequency and duty cycle to alternately charge and discharge an inductor having one end connected to a power supply voltage and its other end connected to the transistor. The transistor is connected between ground and the inductor. An output filter and diode are connected to the inductor so that, when the transistor is off, the inductor incrementally charges an output filter capacitor. The amount of charge per cycle equals the current needed by the load, connected to the output filter, so that the regulator supplies current to the load at a constant voltage. A feedback circuit varies the duty cycle to keep the output voltage at the desired regulated voltage.
The typical boost regulator chip requires an input voltage of at least 2.5 volts for operating its control circuitry. Since most batteries used in portable electronic devices housing a boost regulator are 1.5 volts, such devices require at least two batteries in order to supply sufficient operating voltage to the boost regulator. Further, as the batteries age and lose energy, their output voltage will drop so that the batteries need replacing when their combined voltage is less than 2.5 volts.
What is desirable is a boost regulator circuit that can operate with battery voltages of 1.5 volts or less so that only one battery is needed to operate the boost regulator.